ABSTRACT: BACKGROUND:Over the past several decades, treatment of cancer in adolescents and young adults (AYAs) has evolved substantially, leading to steady improvements in estimated 5-year survival at diagnosis. However, the impact on late mortality in this population is largely unexamined. We investigated temporal trends in mortality among 5-year AYA cancer survivors. METHODS:The Surveillance, Epidemiology, and End Results database was used to identify AYAs (age 15-39 years) diagnosed with cancer during 1975-2011 who survived at least 5?years beyond diagnosis. Survival months were accrued from 5 years postdiagnosis until death or the end of 2016. Cumulative mortality from all causes, the primary cancer, other cancers, and noncancer or nonexternal causes (ie, excluding accidents, suicide, homicide) were estimated according to diagnosis era. RESULTS:Among 282?969 five-year AYA cancer survivors, 5-year mortality (ie, from 5 through 10?years postdiagnosis) from all-causes decreased from 8.3% (95% confidence interval = 8.0% to 8.6%) among those diagnosed in 1975-1984 to 5.4% (95% confidence interval = 5.3% to 5.6%) among those diagnosed in 2005-2011. This was largely explained by decreases in mortality from the primary cancer (6.8% to 4.2%) between these periods. However, for specific cancer types, including colorectal, bone, sarcomas, cervical/uterine, and bladder, cumulative mortality curves demonstrated little improvement in primary cancer mortality over time. Some reduction in late mortality from noncancer or nonexternal causes was apparent for Hodgkin lymphoma, leukemia, kidney cancer, head and neck cancers, and trachea, lung, and bronchus cancers. CONCLUSION:Over the past four decades, all-cause and cancer-specific mortality have decreased among 5-year AYA cancer survivors overall, but several cancer types have not shared in these improvements.